ENERGY STAR qualified windows, doors, and skylights save energy and money, increase the comfort of your home, and protect your valuable possessions from sun damage. When you lower your energy use, you lower the amount of air pollution generated by electric power plants, making efficient windows environmentally friendly.
NFRC is a non-profit organization that administers the uniform, independent rating and labeling system for the energy performance of windows, doors, skylights, and attachment products.
Rating Window Efficiency Systems
When you look at different window models it is important to evaluate the manufacturer’s U-Value and R-Value ratings.
The U-Value is a measurement of heat conductance. It indicates a window’s tendency to transfer heat either in or out of your home. A window with a low U-Value will lose less heat than one with a higher U-Value.
The R-Value is a measurement of heat flow resistance. A window with a high R-Value will lose less heat than a window with a lower R-Value.
Most window manufacturers use R-Values when rating their windows. Window R-Values typically range from 0.9 to 3.0. U-Values usually range from 1.1 to 0.3.
How to Compare Energy Efficiency Values for Different Windows
When comparing different windows, you should ensure that all U-Values or R-Values listed by manufacturers are:
- Based on current standards
- Calculated for the entire window, including the frame, and not just for the center of the glass
- Representative of the same window size and style
Factors Affecting the R-Value of Windows
- Type of glazing material (glass, treated glass, plastic, etc.)
- Number of layers of glass
- Size of the air space between the layers of glass
- Thermal resistance of conductance of the frame and spacer materials
- Tightness of the installation